Copper oxide disk and method of making same



Feb. 24, 1942. D, w, RANDOLPH TAL 2,273,991

COPPER OXIDE DISK AND METHOD OF MAKING SAME 2 Sheets-Sheet 1 AMPLIFIER PRESSURE REDUCER VALVE MPRESSED AIR L//YE Feb. 24, 1942. D. w. RANDOLPH ErAL 2,273,991

COPPER OXIDE DISK AND METHOD OF MAKING SAME Patented Feb. 24, 1942 `COPPER OXIDE DISK AND METHOD OF MAKING SAME Donald W. Randolph and Robert H. Bigler, Flint,

Mich., assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application April 27, 1938, Serial No. 204,703

11 Claims.

This invention relates to the manufacture of a copper oxide disk or button, and has particular adaptation or use in connection with the temperature indicator on intemal combustion engines of automotive vehicles.

The present application is an improvement on the method described and claimed in our Patent 2,197,115, April 16, 1940.

In investigating the installation of temperature indicators of the type shown and described in our above-mentioned patent, further researches were made to improve the character and constancy of the copper oxide disk or button used in the engine unit of the indicator. For instance, the button of the prior patent has no metallic coating, while the button of this application has sprayed thereon a coating of copper on the side which has the copper oxide coating. This copper spraying, it has been found, gives a more intimate contact and enables a more ready passage of current through the button.

The buttons or disks of the invention are prepared from copper and are preferably stamped from a sheet of sheet copper although they may be prepared in any suitable way. The buttons are then fiat ground on one side and etched in a weak solution of nitric acid for a short period of time in order to obtain a perfectly clean fresh copper surface, and are then Washed in running water. After washing in water and before placing in the furnace they are kept under denatured alcohol in order to keep the surfaces clean. When the furnace is ready to receive the disk or buttonl the buttons are taken from under the alcohol and placed in a pan in the furnace, and the furnace temperature kept at about 900 C. While the buttons are in the furnace, tank nitrogen which contains about 0.2% of oxygen by volume, is passed therethrough and owing to the heated state of the copper, the buttons are gradually and uniformly oxidized. Tank nitrogen is used in order to retard or reduce the rate of oxidation during the period while the buttons or disks attain furnace temperature; and also because of the low cost of tank nitrogen. This tank nitrogen is passed through the furnace for about fifteen minutes and then air is admitted for about five minutes, making a total time of twenty minutes in the furnace for the disks. are then removed and allowed to cool in air and after cooling they have a comparatively heavy coating of red copper oxide, and a surface of jet black oxide. Care is taken not to touch or damage the black oxide surface in any way during subsequent handling.

The disks The disks or buttons are next heated to about 200 C. and maintained at that temperature while a thin coating of copper is sprayed on one side of the buttons, the copper being sprayed by the use of a metal spray gun. The effect of heating the pellet during the spraying is to obtain a more uniform adherent copper coating.

The oxide film or coating on the disk is next removed from the side which does not have the copper coating. 'I'his is removed by grinding on a sander. The button or disk is then placed in a fixture and subjected to a temperature of about C. while a current of 0.8 ampere is passed through the disk for a period of about fteen minutes. This latter step serves both as an ageing treatment and as a test for disks which are electrically weak. The temperature of 160 C. is maintained because we found this temperature, coupled with the indicated current and the time, to give the best stability in use.

On removing the disk from the ageing fixture, the disk is transferred to a calibrating fixture in which the disk is held at a temperature of about 82 C. (180 F.). While adjustment in calibration is made, a portion of the copper coating is removed. The disks may be calibrated at'any temperature but we found 82 C. a convenient point on the scale. Units made by this process are sui'liciently uniform so that calibration at one point automatically gives satisfactory adjustment at all other points on the temperature scale. The calibration of the disks comprises the process or change necessary to make the disks conform to a prototype or standard. The disks must be interchangeable; each must have the same electrical characteristics which accompany temperature changes; and the calibration is the reduction of all of them to a given standard. The calibration includes the step of removing part of the sprayed copper.

On the drawings:

Figure 1 is a more or less diagrammatic view of the electrical furnace in which the disks are oxidized.

Figure 2 is a sectional view through the furnace of Figure 1.

Figure 3 is a side view of the spray gun and fixture showing the manner in which the copper oxide coated disks are sprayed with a copper spray.

Figure 4 is a sectional view through a part of the engine and the engine unit of the temperature indicator, showing the application of the copper oxide disk.

Figure 5 is an enlarged detailed view of the inside end of the engine unit of the temperature indicator.

Figure 6 is a view of a part of an automobile showing the invention installed.

Referring to Figure 1, the electrical connections 2 as shown are merely in diagrammatic form to cover a conventional electric furnace controlled circuit. The controller l is a standard potentiometer instrument which turns the current in the furnace winding oil and on to maintain a constant furnace temperature as indicated by the thermo-couple O. .The controller accomplishes this constant temperature operation by opening and closing the contactor indicated as a whole at I. .The twenty-ohm rheostat Il is included to assist the controller in maintaining close regulation.

A gas line i2, which obtains tank nitrogen from the container il, is provided with a restriction at il. A pressure reducer valve Il is provided between the tank i4 and the line i2 and a branch line 2l controlled by a valve 22 leads to a compressed air reservoir (not shown). A valve u controls the line I2 and may connect it either to the tank I4 or to the compressed air line 2l.

The purpose of the restriction il is to develop a sufiicient pressure drop to indicate on the manometer 2t. Since the size of the restriction Il is fixed, the manometer may be calibrated in the terms of amount of gas flow per minute. The

manometer is actually calibrated in cubic feet per minute. If the manometer setting is reproduced each time the furnace is used, then the rate of gas flowing through the furnace is constant or duplicated for each heating.

The furnace is indicated as a whole at 28 and comprises the outer shell l in which there is applied the refractory lining 32. The inner refractory member or tube u of the furnace is preferably circular, as shown in detail in Figure 2, and is adapted to receive a removable tray I0 on which the buttons or disks 3l are received. 'I'his tube 34 projects from both sides of the furnace and its extreme right hand end is closed by means of the cork plug ll which has. a central opening to receive the end of the tube or line I2. A little beyond the plug l0 a porousor refractory baille 44 is placed in the tube Il. This bame 44 is very porous and serves to protect the cork plug 4I in the end of the furnace tube fromV the heat radiated from the inside of the furnace. The porous baille also acts as a distributor for the gas entering the furnace and insures its more uniform distribution over the cross section of the furnace tube.

At the left side of the furnace the tube 34 is provided with a closure I6, which has a central opening for receiving the end of the tube or line 4I. This tube or line 48 delivers into a bottle or trap 50 which has a quantity of water 52 therein. A second tube 84 fitted in the cork 5l of the bottle 5l allows the escape of gas to the outside. 'I'his trap is merely to indicate that there is no leak in the furnace and insures the furnace against leakage inward as the pressure inside the furnace must be greater than atmospheric by the height of the water in the trap.

The usual electric coil or wire around the furnace tube Il is indicated at 58.

In Figure 3 the gun It to apply the coating of molten copper to the buttons after they come from the furnace is shown. This gun forms no Dart of the invention and is not illustrated in detail. The gun is known as the multiplex metal ,avaoor spray gun, manufactured by the winism M. Brita ton Company. Detroit, Michigan. The gun feeds, melts. and atomizes the copper wire and deposits the molten metal in a dense coating of any thickness upon the buttons or disks. The multiplex metal spray gun feeds a metal wire to a burner having several jets of oxy-acetylene flame. The

wire is melted and the molten metal is finely atomized by compressed air and deposited upon the surface to be coated in a solid body of metal of any thickness required. The power required to feed the wire to the burner is obtained from a small positive pressure air motor, the speed of which is controlled by a throttle, The oxy-acetylene burner, the air motor. the wire feed-rolls, and the speed reducing gears required, are all incorporated in the construction of the metal spray gun. The sprayed metal is not fused to the surface coated, but the extremely small molten particles of metal cling tightly to the surface coated and to each other due to the high velocity of impact and the slightly roughened surface, and produce a solid body of metal which may be machined, ground or polished.

At the left of Figure 3, a fixture l2 is shown. This fixture has an opening Il in its top, the opening being tapered as indicated at 86, and is provided with a shoulder Il on which the buttons Il are received. The button Il is held in place by means of a lever 'Il pivoted at 12 to the fixture I2. A spring 'Il holds the lever 1l in the position shown in Figure 3. To release the lever, the operator presses on the free end 'it to swing the opposite end away from the disc Il.

By referring to the position of the disk 3l in the fixture 02 it will be noted that the shoulder ll serves as an annular mask for the edge of the button and prevents any molten copper from being sprayed on the edges of the disk. The copper is therefore sprayed on the center of the disk only.

In Figure 4 there is shown in sectional detail the application of the engine unit of the heat indicator to an internal combustion engine. The wall of the engine, indicated. at 1I, is provided with a threaded opening to receive the threads Il of a plug or unit l2. This plug or unit has a reduced inner end .I over which there is fitted the cap Il, secured in place by means of solder Il. This cap is of metal, such as copper. Any other means of securing the cap in place may be used. The plug 82 is hollow and on its inside is provided with the insulating cylinder I0. 'l'his cylinder extends from the cap 86 for substantially the full inner length of the plug 82.

At the extreme inside of the bore of the plug, one of the disks Il of the invention is mounted as shown in the figure. 'I'his disk has its innermost surface ground clear of the copper oxide coating to give a bright copper surface, but the copper oxide coating still remains on the edge and on the other side of the disk. This copper oxide coating is indicated at 92 and has the copper coating il sprayed thereon. Over the copper coating there is a film or layer 9! of graphite to give an intimate contact between the copper coating and a disk of pure copper llt. A coil spring il! is received inside the insulating cylinder ll and at its inner end contacts with the disk i" and at its outer end with a disk I formed integral with the contact III, positioned at the outer end of the plug I2. The contact |08 has a threaded shank III and over the shank |08 the insulating washer Ill is positioned. Over the washer IIIY the retaining element Il! is received and this retaining element fits in a recess in the end of plug 62 and is held in position by the turned over metal ||4. A second insulating washer ||6 is placed on shank and fits into an opening in the retainer ||2 and a third outer insulating washer ||0 is positioned over the washer ||6 and over the retainer ||2. A metal washer is positioned on the shank |06 and rests against the washer ||0. A nut |22 is threaded on the shank |00 and holds the parts together as shown in Figure 4. A wire |24 has its end |26 positioned over the shank |06 and is held in place by means of the lock nut |26.

`A coat of insulating varnish is added to the joint at the turned over metal ||4 of the plug 02. This varnish is added after the crimping operation and is for the purpose of making the unit weatherproof. f

In Figure 6 the application of the heat indicator to the internal combustion engine of an automotive vehicle is shown. The vehicle is indicated as a whole at |26. The vehicle has the roof |26, the windshield |30, the hood |32, instrument board |34, and the engine block |36.

The engine block is provided with the usual head as leading from a differential galvanometer on the instrument board |34, to the plug B2 in the engine block. A wire |52 leads to the ignition switch |54, and a third wire |56 leads from the ignition switch to the battery |56 which is grounded as indicated at |60.

The copper oxide button 38 of the invention has the characteristic of changing its electrical conductivity with a change in temperature. That is, the higher the temperature, the greater the conductivity, and where the disk will allow the passage of the current with diillculty, or not at all, at lower temperatures, the passage of current is facilitated by an increase in the ternperature of the copper oxide disk. For temperatures within the range desired for an internal combustion engine of an automotive vehicle, for instance, the change in electrical conductivity from about 100 F. to 212 F. is substantially uniform so that by Calibrating the differential galvanometer to read directly in temperatures, the temperature of the water cooling system may be read directly. This operation'is the same as that described in our Patent 2,197,115, issued April 16, 1940.

We claim:

1. The method of making a copper oxidized button and stabilizing it with reference to uniformity of resistance changes with temperature changes between substantially 100 and 212 F., consisting of punching a button from a sheet of copper, flat grinding the button clean on one side, etching the button in 10% nitric acid for about forty-five seconds, then washing in running water, then placing the button under denatured alcohol, then in placing the button in a furnace having a temperature of about 900 C., passing tank nitrogen through the furnace for a period of about fifteen minutes, then admitting atmospheric air to the furnace for about five minutes, then removing the button from the furnace and allowing it to cool in the air, then heating the button to about 200 C., then in spraying the face of the button with a coating of copper while the temperature is maintained at 200 C., then in rebutton, then in placing the button in a fixture and maintaining the button at substantially 160 C. and passing an electric current of approximately .8 ampere through the button for about fifteen minutes, then calibrating the button by maintaining the button at a predetermined temperature and removing a portion of the copper coating to bring the electrical resistance of the button to-a standard.

2.'The method of making a copper oxidized copper object and stabilizing it with reference to uniformity of resistance changes with temperature changes between substantially 100 and 212 F., consisting of forming the article, grinding the object clean on one side, etching the object in a dilute solution of nitric acid for a short period of time, then washing in water, then placing the object under alcohol, then in placing the article in a furnace and subjecting it to a temperature high enough to form an oxide of copper thereon, passing nitrogen with a small quantity of oxygen through the furnace for a period of about fifteen minutes, then admitting atmospheric air to the furnace for about five minutes, then removing the object from the furnace and allowing it to cool, then heating the object, then in applying a coating of copper to the face of the object while the temperature is maintained, then in removing the oxidized coating from one side of the object, then in passing a low amperage electric current through the object for about fifteen minutes while maintaining the object in a heated state, then in Calibrating the object in a heated state.

3. The method of preparing a copper oxidized copper object for commercial use, consisting of heating the object to about 200 C., then in spraying the face of the object with a coating of molten copper while the temperature is maintained at about 200 C., then in removing the oxidized coating from the back of the object, then in placing the object in a fixture and maintaining the object at substantially 160 C. and passing an electric current of approximately .8 ampere through the object for about fifteen minutes, and then in calibrating the object by heating the object to a predetermined temperature and removing a portion of the copper coating to bring the electrical resistance of the object to a standard.

4. The method of preparing Aa-copper oxidized copper object for commercial use consisting of heating the object, then in giving a good electrically conductive surface to the object by spraying the face of the object with a coating of molten copper while the object is maintained in a heated moving the oxidized coating from the back of the state, then in removing the oxidized coating from the back of the object, then in passing a low amperage electric current through the object for a substantial period of time, then in calibrating the object while maintaining the object in a heated state to cause the object to conform to a standard.

5. The method of making a copper oxide button or disk and stabilizing it with reference to uniformity of resistance changes with temperature changes between substantially and 212 F., consisting of forming a pellet of copper, grinding the button or disk clean on one side, etching the pellet in dilute nitric acid for a short period of time, then washing in water, then placing the pellet in alcohol, then in placing the pellet in a furnace maintained at a temperature high enough to form an oxide of copper on the button or pellet, passing tank nitrogen through the furnace for a period of time. then admitting atmospheric air to the furnace for an additional period of time, then removing the pellet from the furnace and allowing it to cool.

6. The method of making a copper oxidid button and stabilizing it with referencey to uniformity of resistance changes with temperature changes between substantially 100 and 212 F., consisting of punching a button from a sheet of copper, flat grinding the button clean on one side, etching the button in nitric acid for about forty-five seconds, then washing in running water, then placing the button under denatured alcohol, then in placing the button in a furnace having a temperature of about 900 C., then passing tank nitrogen through the furnace for a period of about fifteen minutes, then admitting atmospheric air to the furnace for about five minutes. then removing the button from the furnace and allowing it to cool in the air.

7. The method of making a copper oxidized button and stabilizing it with reference to uniformity of resistance changes with temperature changes between substantially 100 and 212 F., consisting of forming a button of copper, etching the button in dilute nitric acid solution for about forty-five seconds, then washing in water, then placing the button in alcohol, then in placing the button in a furnace and heating the furnace to a temperature of about 900 C., passing nitrogen diluted with a small amount of oxygen through the furnace for an appreciable period of time,

then admitting atmospheric air to the furnace for an additional period of time, removing the button from the furnace and allowing it to cool, then heating the button, then in spraying one faceof the button with a coating of copper while the temperature is maintained, then in removing the oxidized coating from the other face of the button, and then in passing an electric current of approximately .8 ampere through the button foxl a substantial period of time and calibrating the button while a current is passing therethrough.

y8. 'Ihe method of making a copper oxidized button and stabilizing it with reference to uniformity of resistance changes with temperature changes between substantially 100 and 212 F., consisting of forming a button of copper, etching allowing ittocoolintheair.

9. The method of preparing a copper oxidized copper button for commercial use, consisting of heating the button to about 200 C., then in spraying the face cf the button with a coating of fused copper while the temperature is maintained at about 200 C., then in removing the oxidized coating from the back of the button, then in heating the button and maintaining it at substantially 160 C. and passing a low amperage electric current through the button for about nfteen minutes, then in heating the button to a predetermined temperature, and maintaining it at this temperature while removing a portion of the coppercoating to bring the electrical resistance of the button to a standard y l0. The method of preparing a copper oxidized copper object for commercial use, consisting in forming the object, processing the object to give to it a coating of an oxide of copper having a constancy of change in resistance with changes in temperature between substantially and 212 F., placing the object in a fixture, shielding the edge of one face of the object, and then giving a good electrically conductive ysurface to the object by applying molten copper to the face of the object having the shielded edge.

11. An article of manufacture comprising a copper object having thereon on one face only a processed coating of an oxide of copper having substantially constant changes in electrical resistance with changes in temperature between substantially 100 Aand 212 F., a coating of copper applied in afused state to the object on the face having the coating of4 an oxide of copper, and a border or margin at the fused copper applied side of the object over which no copper is applied.

. DONALD W. RANDOLPH.

ROBERT H. BIGLER. 

